When radiochemistry meets radioecology (the marine environment).

After the first atomic bomb test in Alamogordo in July 1945, followed by the Hiroshima and Nagasaki bombs in August 1945, radioecology became recognized as a branch of ecology in response to the radioactive fallout associated with the subsequent proliferation of atmospheric nuclear weapons testing which continued throughout the Cold War. In parallel, environmental radiochemistry emerged in the 70s to understand the chemical behavior of possible nuclear contaminants of the environment. In this discussion we stress the need to crosslink radioecology and chemical speciation, where radiochemistry and radioecology should meet to go beyond the present state of the art. Accordingly, we are seeking a methodology that calls for several angles of investigation: speciation (chemistry), toxicology (physiology and biology), accumulation data (environmental studies), distribution (geochemistry).

Uranium contamination of bivalve Mytilus galloprovincialis, speciation and localization.

Uranium is a natural radioelement (also a model for heavier actinides), but may be released through anthropogenic activities. In order to assess its environmental impact in a given ecosystem, such as the marine system, it is essential to understand its distribution and speciation, and also to quantify its bioaccumulation. Our objective was to improve our understanding of the transfer and accumulation of uranium in marine biota with mussels taken here as sentinel species because of their sedentary nature and ability to filter seawater. We report here on the investigation of uranium accumulation, speciation, and localization in Mytilus galloprovincialis using a combination of several analytical (Inductively Coupled Plasma Mass Spectrometry, ICP-MS), spectroscopic (X ray Absorption Spectroscopy, XAS, Time Resolved Laser Induced Fluorescence Spectroscopy, TRLIFS), and imaging (Transmission Electron Microscopy, TEM, µ-XAS, Secondary Ion Mass Spectrometry, SIMS) techniques. Two cohorts of mussels from the Toulon Naval Base and the Villefranche-sur-Mer location were studied. The measurement of uranium Concentration Factor (CF) values show a clear trend in the organs of M. galloprovincialis: hepatopancreas â‰« gill > body ≥ mantle > foot. Although CF values for the entire mussel are comparable for TNB and VFM, hepatopancreas values show a significant increase in those from Toulon versus Villefranche-sur-Mer. Two organs of interest were selected for further spectroscopic investigations: the byssus and the hepatopancreas. In both cases, U(VI) (uranyl) is accumulated in a diffuse pattern, most probably linked to protein complexing functions, with the absence of a condensed phase. While such speciation studies on marine organisms can be challenging, they are an essential step for deciphering the impact of metallic radionuclides on the marine biota in the case of accidental release. Following our assumptions on uranyl speciation in both byssus and hepatopancreas, further steps will include the inventory and identification of the proteins or metabolites involved.

Bond-bending isomerism and metallophilicity in metal-halogen anions (Cu,Ag,Au)2X3 -, X = F, Cl, Br, I, At.

In the framework of DFT (ABINIT package), we have performed atomic relaxations on the (Cu,Ag,Au)2X3 -, X = F, Cl, Br, I, At anion series. Opposite to linear (MX2)- anions, all (M2X3)- systems are triangular (C 2v symmetry). According to the system, we classified these anions in three categories according to the relative strength of electronegativity, chemical hardness, metallophilicity and van der Waals interaction. We found two bond-bending isomers: (Au2I3)- and (Au2At3)-.

Aquatic Chemistry of Pentavalent Plutonium: Determination of the First Hydrolysis Constant.

Up to now, no recommendations have been made by the Organisation for Economic Co-operation and Development Nuclear Energy Agency (OECD-NEA) for the first two hydrolysis constants of pentavalent plutonium. We have determined them, as well as those of Np(V), by means of capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) in 0.1 M NaCl at 25 °C. The hydrolysis constants of Pu(V) were compared to those of Np(V), for which consensual values have been proposed by the OECD-NEA. The first hydrolysis stability constant for Pu(V) extrapolated at zero ionic strength (log⁡ß10*=-(11.50±0.12)) is, as expected, close to that of Np(V) (log⁡ß10*=-(11.36±0.13)). We have obtained an excellent agreement with the OECD-NEA value for Np(V) [log⁡ß10*=-(11.3±0.7)]. Based on eight independent values including our own, we propose a new, robust value for the first hydrolysis of Np(V): log⁡ß10*=-(11.22±0.20). The determination of the second hydrolysis constant for Np(V) by CE-ICP-MS [⁢log⁡ß20*=-(24.40±0.33)] deviates from the value adopted by the OECD-NEA [⁢log⁡ß20*=-(23.6±0.5)]. This discrepancy might be explained by the association of a sodium counter cation with the species [NpO2(OH)2]-. A stability constant is proposed at zero ionic strength and 25 °C for this association: log⁡KNa[NpO2(OH)2]0=(1.6±0.5). As a result, it is considered that the second hydrolysis constant for Pu(V), [⁢log⁡ß20*=-(24.24±0.26)], is also a mixed constant, taking into account both the hydrolysis and the association with a sodium cation.

Xe Adsorption on Noble Metal Clusters: A Density Functional Theory Investigation.

The adsorption mechanism of xenon on three noble metal clusters (M = Ag, Au, and Cu) has been investigated in the framework of density functional theory (DFT) within generalized gradient approximation (GGA-PBE). The ab initio calculations were performed with the quantum molecular dynamics (QMD) package ABINIT using the projector augmented (PAW) formalism. The spin-orbit coupling (SOC) and dispersion effects (Van der Waals DFT-D3) have been taken into account. According to these calculations, the M-Xe bonds are partly covalent and electrostatic and their contribution depends on the cluster size and nature. This study underlines the importance of using the SOC and the Van der Waals (VdW) effects. Based on these results, copper nanoparticles have the highest affinity for interaction with xenon compared with silver and gold.

Carboxylate- and Phosphonate-Modified Polyethylenimine: Toward the Design of Actinide Decorporation Agents.

Plutonium (Pu) is an anthropogenic element involved in the nuclear industry cycle. Located at the bottom of the periodic table within the actinide family, it is a chemical toxic but also a radiological toxic, regardless of isotopy. After nearly 80 years of Pu industrialization, it has become clear that inhalation and wounds represent the two main ways a person may become contaminated after an accident. In order to reduce the deleterious health effects of Pu, it is crucial to limit chronic exposure by removing it or preventing its incorporation into the body. Diethylenetriaminepentaacetic acid (DTPA) has emerged as the gold standard for Pu decorporation, although it suffers from very short retention time in serum. Other molecules like the hydroxypyridonate family with high chemical affinity have also been considered. We have been considering alternative polymeric chelates and, in particular, polyethylenimine (PEI) analogues of DTPA (the carbonate or phosphonate version), which may present a real breakthrough in Pu decorporation not only because of their higher loading capacity but also because of their indirect vectorization properties correlated with a specific biodistribution into the lungs, bone, kidney, or liver. In the first part of this Forum Article, new data on the structural characterization of the complexation of PuIV with polyethylenimine methylphosphonate (PEI-MP) were obtained using the combination of extended X-ray absorption fine structure spectroscopy and ab initio molecular dynamics (AIMD) calculations. The use of thorium (Th) as a Pu chemical surrogate is also discussed because its unique oxidation state is IV+ in solution. In the second part of the paper, we put this new set of data on PEI-MP-Pu into perspective with use of the PEI platform to complex ThIV and PuIV. Uptake curves of ThIV witth polyethylenimine methylcarboxylate (PEI-MC) are compared with those of PEI-MP and DTPA, and the AIMD data are discussed.

Fetuin exhibits a strong affinity for plutonium and may facilitate its accumulation in the skeleton.

After entering the blood, plutonium accumulates mainly in the liver and the bones. The mechanisms leading to its accumulation in bone are, however, completely unknown. We already know that another uptake pathway not involving the transferrin-mediated pathways is suspected to intervene in the case of the liver. Fetuin, a protein playing an important role in bone metabolism, is proposed as a potential transporter of Pu from serum to bone. For the first time, the binding constants of these two proteins (transferrin and fetuin) with tetravalent plutonium at physiological pH (pH 7.0) were determined by using capillary electrophoresis (CE) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Their very close values (log10 KPuTf = 26.44 ± 0.28 and log10 KPuFet = 26.20 ± 0.24, respectively) suggest that transferrin and fetuin could compete to chelate plutonium, either in the blood or directly at bone surfaces in the case of Pu deposits. We performed competition reaction studies demonstrating that the relative distribution of Pu-protein complexes is fully explained by thermodynamics. Furthermore, considering the average concentrations of transferrin and fetuin in the blood, our calculation is consistent with the bio-distribution of Pu observed in humans.

Is hydroxypyridonate 3,4,3-LI(1,2-HOPO) a good competitor of fetuin for uranyl metabolism?

Uranium is widespread in the environment, resulting both from natural occurrences and anthropogenic activities. Its toxicity is mainly chemical rather than radiological. In the blood it is transported as uranyl UO22+ cation and forms complexes with small ligands like carbonates and with some proteins. From there it reaches the skeleton, its main target organ for accumulation. Fetuin is a serum protein involved in biomineralization processes, and it was demonstrated to be the main UO22+-binder in vitro. Fetuin's life cycle ends in bone. It is thus suspected to be a key protagonist of U accumulation in this organ. Up to now, there has been no effective treatment for the removal of U from the body and studies devoted to the interactions involving chelating agents with both UO22+ and its protein targets are lacking. The present work aims at studying the potential role of 3,4,3-LI(1,2-HOPO) as a promising chelating agent in competition with fetuin. The apparent affinity constant of 3,4,3-LI(1,2-HOPO) was first determined, giving evidence for its very high affinity similar to that of fetuin. Chromatography experiments, aimed at identifying the complexes formed and quantifying their UO22+ content, and spectroscopic structural investigations (XAS) were carried out, demonstrating that 3,4,3-LI(1,2-HOPO) inhibits/limits the formation of fetuin-uranyl complexes under stoichiometric conditions. But surprisingly, possible ternary complexes stable enough to remain present after the chromatographic process were identified under sub-stoichiometric conditions of HOPO versus fetuin. These results contribute to the understanding of the mechanisms accounting for U residual accumulation despite chelation therapy after internal contamination.

Determination of the isotopic composition of single sub-micrometer-sized uranium particles by laser ablation coupled with multi-collector inductively coupled plasma mass spectrometry.

RATIONALE: A multi-collector inductively coupled plasma (MC-ICP) mass spectrometer coupled to a UV ns-laser ablation (LA) system was used to measure uranium isotopic ratios (234 U/238 U, 235 U/238 U and 236 U/238 U) in single uranium particles of various sizes and isotopic compositions, including home-made sub-micrometric natural uranium particles of narrow size distribution (415 ± 60 nm). METHODS: The LA-ICP mass spectrometer was operated in wet plasma conditions thanks to simultaneous injection of the laser aerosol and water vapor through a desolvating nebulizer. The isotopic ratios were corrected for mass bias and gain factors between detectors. The 236 U/238 U ratios were also corrected for the presence of 235 U hydrides and tailing of the 238 U+ peak. RESULTS: 236 U/238 U ratios were successfully measured in micrometer-sized particles from the NBS U050 certified standard material with a 236 U/238 U ratio of ~5 × 10-4 . The analysis of 77 natural uranium sub-µm-sized particles yielded a very good trueness with respect to the expected 234 U/238 U and 235 U/238 U ratios, while the measurement errors for single particles ranged from -2.7% to +2.1% for 235 U/238 U and from -17% to +33% for the 234 U/238 U ratios. Their relative combined standard uncertainties ranged from 3.3% to 32.8% and from 0.4% to 4.0% for 234 U/238 U and 235 U/238 U ratios, respectively. In addition, extremely low detection limits, in the attogram range, were achieved. CONCLUSIONS: This study demonstrates that coupling of a ns-laser ablation system with a MC-ICP mass spectrometer allows measurements of the isotopic composition in natural uranium particles of a few hundreds of nm with very good trueness, average combined standard uncertainties of ~1% for 235 U/238 U ratios and 12% for 234 U/238 U ratios, and detections limits of a few ag for minor isotopes.

Polyethyleneimine methylenecarboxylate: a macromolecular DTPA analogue to chelate plutonium(iv).

Up until now, molecular chelating agents, such as diethylenetriamine pentaacetic acid (DTPA), have been the standard method for actinide human decorporation. Mainly active in blood serum, their distribution within the body is thus limited. To treat a wider range of organs affected by plutonium contamination, a potential new class of macromolecular decorporation agents is being studied. Polyethyleneimine methylenecarboxylate (PEI-MC) is one such example. It is being considered here because of its capacity for targeting the liver and bones.

Towards the development of chitosan nanoparticles for plutonium pulmonary decorporation.

Since the 1940s, great amounts of Plutonium (Pu) have been produced for both military and civil purposes. Until now, the standard therapy for decorporation following inhalation has been the intravenous injection of diethylenetriaminepentaacetic acid ligand (Ca-DTPA form). This method offers a strong complexing constant for Pu(iv) but has poor chemical specificity, therefore its efficacy is limited to actinides present in the blood. Consequently, there is no decorporation treatment currently available which efficiently removes the intracellular Pu(iv) trapped in the pulmonary macrophages. Our research shows that a nanoparticle approach could be of particular interest due to large contact area and ability to target the retention compartments of the lungs. In this study, we have focused on the inhalation process involving forms of Pu(iv) with poor solubility. We explored the design of biocompatible nanoparticles able to target the macrophages in the lung alveoli and to chelate the forms of Pu(iv) with poor solubility. Nanoparticle formation was achieved through an ionic cross-linking concept using a polycationic polymer and an anionic chelate linker. We chose N-trimethyl chitosan, for its biocompatibility, as the polycationic polymer base of the nanoparticle and the phosphonic analogue of DTPA, diethylenetriamine-pentamethylenephosphonic acid (DTPMP) as the anionic chelating linker in forming NPs TMC-DTPMP. The synthesis and physico-chemical characterization of these NPs are presented. Secondly, the complexation mechanisms of TMC-DTPMP NPs with Thorium (Th(iv)) are discussed in terms of efficiency and structure. The Extended X-Ray Absorption Fine Structure (EXAFS) of the TMC-DTPMP complex with Th(iv) as well as Pu(iv) are defined and completed with DFT calculations to further delineate the plutonium coordination sphere after complexation. Finally, preliminary cytotoxicity tests onto macrophages were assayed.

Topological speciation of actinide-transferrin complexes by capillary isoelectric focusing coupled with inductively coupled plasma mass spectrometry: evidence of the non-closure of the lobes.

The determination of the binding constant between transferrin and thorium and the conformational changes of the protein upon metal complexation (thorium and plutonium) have been studied by both capillary electrophoresis (CE) and capillary isoelectric focusing (cIEF) coupled with inductively coupled plasma mass spectrometry (ICP-MS). This method allows the use of both the separation power of the cIEF and the low detection limit of ICP-MS which is critical when working with highly radioactive elements. To our knowledge, this is the first time a method coupling cIEF and ICP-MS is reported in the literature. Nitrilotriacetate was used to prevent from actinide hydrolysis and as a competitive ligand with transferrin. The binding constant for the complexation of transferrin and thorium, in the absence of bicarbonate at pH 7, was found to be log K = 18.65 ± 0.19. This value, close to that of transferrin with iron, evidenced the high affinity of the protein for thorium. The results obtained by the newly developed method, cIEF-ICPMS, showed no pI change after the addition of thorium or plutonium, whereas a pI shift (linked to conformational changes) occurred for the transferrin-indium complex. This suggests that, despite the high affinity towards the actinides, the protein does not undergo a significant structure change upon complexation. The important ionic radius of the cations Th4+ (1.05 Å, CN = 8) and Pu4+ (0.96 Å, CN = 8) with respect to Fe3+ (0.645 Å, CN = 6) and to a lesser extent to In3+ (0.800 Å, CN = 6) suggests that the transferrin lobe does not close completely after complexation. However, mixed indium-actinide complexes showed structural changes even at high concentrations of apotransferrin. The conformational change is not governed by the actinide but by the other metals present.

Evidence for the Heaviest Expected Halide Species in Aqueous Solution, At-, by Electromobility Measurements.

At- (astatide) is commonly expected to be the heaviest halide in the halogen group. However, there is no proof for the existence of this -1 charged species. Furthermore, investigations with astatine are restricted by its specific radioactive properties, which entail working at ultratrace concentrations (typically less than 10-10 M). In this work, an especially built electromigration device is applied to obtain information about the charge/size ratio characterizing an ion in aqueous solution. An anionic At species is observed in reducing conditions. Moreover, we propose the first absolute mobility value for the astatine species in acidic reducing condition: (-8.26 ± 0.59) × 10-4 cm2·V-1·s-1. This value appears close to that of I- ((-8.30 ± 0.33) × 10-4 cm2·V-1·s-1), which is obtained by the same method. The similar absolute mobilities obtained for both ions are coherent with theoretical calculations indicating similar diffusion behaviors for At- and I-. This good agreement confirms the existence of the At- species.

Revisiting binding of plutonium to transferrin by CE-ICP-MS.

Capillary electrophoresis coupled with an inductively coupled plasma mass spectrometer was applied for the first time to determine the binding constant of human transferrin (Tf) for tetravalent plutonium. The experiments were carried out in a buffer 2-(N-morpholino)ethanesulfonic acid (MES) at pH 6, 0.1 M NaCl and at a temperature of 25 °C. The nitrilotriacetate anion (NTA) used in this study prevents the hydrolysis of plutonium and is an ideal competitor with Tf for Pu, both ligands sharing comparable binding strength. The separation revealed unambiguous two peaks associated with the complex Pu(NTA)2 used as the initial species and with Pu-transferrin. Two series of independent experiments were conducted and gave the first stepwise conditional bicarbonate-free Pu-transferrin binding constant of . In the absence of bicarbonate the affinity of transferrin for plutonium at pH 6 is about 104 times stronger than that of iron at pH 6.7 .

Optimized measurement of radium-226 concentration in liquid samples with radon-222 emanation.

Measuring radium-226 concentration in liquid samples using radon-222 emanation remains competitive with techniques such as liquid scintillation, alpha or mass spectrometry. Indeed, we show that high-precision can be obtained without air circulation, using an optimal air to liquid volume ratio and moderate heating. Cost-effective and efficient measurement of radon concentration is achieved by scintillation flasks and sufficiently long counting times for signal and background. More than 400 such measurements were performed, including 39 dilution experiments, a successful blind measurement of six reference test solutions, and more than 110 repeated measurements. Under optimal conditions, uncertainties reach 5% for an activity concentration of 100 mBq L(-1) and 10% for 10 mBq L(-1). While the theoretical detection limit predicted by Monte Carlo simulation is around 3 mBq L(-1), a conservative experimental estimate is rather 5 mBq L(-1), corresponding to 0.14 fg g(-1). The method was applied to 47 natural waters, 51 commercial waters, and 17 wine samples, illustrating that it could be an option for liquids that cannot be easily measured by other methods. Counting of scintillation flasks can be done in remote locations in absence of electricity supply, using a solar panel. Thus, this portable method, which has demonstrated sufficient accuracy for numerous natural liquids, could be useful in geological and environmental problems, with the additional benefit that it can be applied in isolated locations and in circumstances when samples cannot be transported.

The pentavalent actinide solution chemistry in the environment.

With regard to environmental monitoring of certain nuclear facilities, pentavalent actinides, in particular neptunium and plutonium, play a key role, as the chief soluble, mobile forms of actinides. In the past five years, investigations carried out by hyphenating capillary electrophoresis to ICP-MS (CE-ICP-MS) have allowed a number of hitherto unknown thermodynamic data to be determined for Np(V) and Pu(V) interactions with the chief environmentally abundant anions. For the first time, data were provided for Pu(V) interactions with carbonate, sulfate, oxalate, chloride, and nitrate ions, allowing the Np(V)/Pu(V) analogy to be verified experimentally. Knowledge of Np(V) chemistry, especially in carbonate, and sulfate media, was also refined. These CE-ICP-MS studies, combined with some earlier findings, have brought about a renewal in the knowledge of An(V) chemistry in solution.

Thermodynamic study of the complexation of protactinium(V) with diethylenetriaminepentaacetic acid.

The complex formation of protactinium(V) with DTPA was studied at different temperatures (25-50 °C) and ionic strengths (0.1-1 M) with the element at tracer scale. Irrespective of the temperature and ionic strength studied, only one neutral complex with (1:1) stoichiometry was identified from solvent extraction and capillary electrophoresis coupled to ICP-MS (CE-ICP-MS) experiments. Density Functional Theory (DFT) calculations revealed that two complexes can be considered: Pa(DTPA) and PaO(H2DTPA). The associated formation constants were determined from solvent extraction data at different ionic strengths and temperatures and then extrapolated to zero ionic strength by SIT methodology. These constants are valid, regardless of complex form, Pa(DTPA) or PaO(H2DTPA). The standard thermodynamic data determined with these extrapolated constants revealed a very stable complex formed energetically by an endothermic contribution which is counter balanced by a strong entropic contribution. Both, the positive enthalpy and entropy energy terms suggest the formation of an inner sphere complex.

Formation of MSeO(4)(aq) complexes (M(2+) = Mg(2+), Co(2+), Ni(2+), Cu(2+), Cd(2+)) studied as a function of temperature by affinity capillary electrophoresis.

Complexation of divalent cations (Mg(2+), Co(2+), Ni(2+), Cu(2+), Cd(2+)) by selenate ligand was studied by ACE (UV indirect detection) in 0.1 mol/L NaNO(3) ionic strength solutions at various temperatures (15, 25, 35, 45 and 55°C). For each solution, a unique peak was observed as a result of a fast equilibrium between the free ion and the complex (labile systems). The migration time corresponding to this peak changed as a function of the solution composition, namely the free and complexed metal concentrations, according to the complexation reactions. The results confirmed the formation of a unique 1:1 complex for each cation. The thermodynamic parameters were fitted to the experimental data at 0.1 mol/L ionic strength: (25°C) = -(6.5 ± 0.3), -(7.5 ± 0.3), -(7.7 ± 0.3), -(7.7 ± 0.3), and -(8.1 ± 0.3) kJ/mol and = 2.5 ± 0.2, 4.7 ± 0.4, 4.5 ± 0.6, 8.4 ± 1.1, and 7.2 ± 0.6 kJ/mol for M(2+) = Mg(2+), Co(2+), Ni(2+), Cu(2+), and Cd(2+), respectively. Complexes with alkaline earth and transition metal cations could be distinguished by their relative stabilities. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at infinite dilution were compared to previously published data on metal-selenate, metal-sulfate, and metal-chromate complexes.

New insights into formation of trivalent actinides complexes with DTPA.

Complexation of trivalent actinides with DTPA (diethylenetriamine pentaacetic acid) was studied as a function of pcH and temperature in (Na,H)Cl medium of 0.1 M ionic strength. Formation constants of both complexes AnHDTPA(-) and AnDTPA(2-) (where An stands for Am, Cm, and Cf) were determined by TRLFS, CE-ICP-MS, spectrophotometry, and solvent extraction. The values of formation constants obtained from the different techniques are coherent and consistent with reinterpreted literature data, showing a higher stability of Cf complexes than Am and Cm complexes. The effect of temperature indicates that formation constants of protonated and nonprotonated complexes are exothermic with a high positive entropic contribution. DFT calculations were also performed on the An/DTPA system. Geometry optimizations were conducted on AnDTPA(2-) and AnHDTPA(-) considering all possible protonation sites. For both complexes, one and two water molecules in the first coordination sphere of curium were also considered. DFT calculations indicate that the lowest energy structures correspond to protonation on oxygen that is not involved in An-DTPA bonds and that the structures with two water molecules are not stable.

Investigation of uranium-colloid interactions in soil by dual field-flow fractionation/capillary electrophoresis hyphenated with inductively coupled plasma-mass spectrometry.

This paper deals with the study of uranium-colloid interactions in a carbonated soil. The work is focused on the immediately available fraction obtained after a leaching process, according to a normalized batch method. In order to characterize the different colloidal carriers, Asymmetrical Flow Field-Flow Fractionation (As-Fl-FFF) coupled to different detectors (UV, Multi Angle Laser Light Scattering (MALLS) and Inductively coupled Plasma-Mass Spectrometry (ICP-MS)) was used. The colloidal carriers are mainly inorganic particles (carbonated particles and clays) mixed with organic substances. Furthermore, dissolved and colloidal uranium species in the leaching solutions were monitored by Capillary Electrophoresis (CE) coupled to ICP-MS, in order to investigate the uranium/colloids interactions. According to the first results, uranium fate in this specific soil is controlled by sorption/desorption phenomena, strongly pH dependent.